The long range goal of this project is to develop an understanding of functional important interactions that occur between proteins and DNA in solution which result in the formation of highly specific complexes. The project will focus on EcoRI methyltransferase and its interaction with target DNA. Methylation performs many functions ranging from protection of host DNA against bacterial restriction endonucleases to the regulation of gene expression in eukaryotes. The EcoRI methyltransferase, which is one of the most characterized methyltransferases, uses the co-factor S adenosylmethionine to methylate the central adenine in the canonical site 5'GAATTC3'. There is considerable evidence that the structure of both the DNA and the methyltransferase are significantly distorted when the complex is formed. The distortions are likely to add specificity to the formation of the complex. A complete description of the distortions and the forces that are required to cause them is not available. The techniques of transient electric birefringence and optical Kerr effect will be used to characterize the mechanical and electrical properties of the methyltransferase and the DNA, separately and in a ternary complex with a co-factor analog. Changes in shape and mechanical stiffness of the methyltransferase upon the addition of co-factors will be determined. We will determine the angle of the putative bend that is induced in the DNA and the position of the methyltransferase relative to the bend. The results will be compared with those for other DNA-protein complexes with an aim of developing a physical model to explain the interactions in solution. The mechanical properties of the methyltransferase will be compared with those of other proteins of similar size that are believed to have elastic hinges between their domains.